Add explanatory comment for 'git tag' command

doc/university/training/topics/tags.md

@@ -28,6 +28,8 @@ git tag my_lightweight_tag
 
 # Annotated tag
 git tag -a v1.0 -m ‘Version 1.0’
+
+# Show list of the existing tags
 git tag
 
 git push origin --tags